| 1. |
- Gu, Jitai, et al.
(author)
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Interdecadal variations in the interannual relationship between winter tropical Pacific SST and subsequent summer Arctic sea ice in early 2000s
- 2024
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In: International Journal of Climatology. - 0899-8418 .- 1097-0088.
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Journal article (peer-reviewed)abstract
- The present study investigates the interdecadal change in the interannual relationship between winter sea surface temperature (SST) in the tropical central-eastern Pacific and the subsequent summer Arctic sea ice concentration (SIC) and its possible mechanism using 1979–2023 monthly SST and SIC data from Hadley Center and atmospheric reanalysis data from NCEP/NCAR. It is found that the relationship between the winter tropical Pacific SST and the subsequent summer SIC of Beaufort Sea experienced an obvious interdecadal change from a significant negative correlation to a weak and insignificant correlation before and after the early 2000s, respectively. Before the early 2000s, when winter SST warming (cooling) anomalies occurred in the central and eastern tropical Pacific, it could sustain into summer and enhance a Rossby wave propagating from Tropic to high latitude, forming negative (positive) pressure anomalies in the North Pacific. Influenced by such anomalies, it is conducive to maintaining negative (positive) SST anomalies in the North Pacific from winter to subsequent summer. The summer SST cooling (warming) in the North Pacific could form a favourable atmospheric circulation anomaly for less (more) SIC. In contrast, after the early 21st century, the strong SST anomalies in winter over the eastern tropical Pacific would weaken with time and subsequently diminish in spring, leading to the SST anomalies in the North Pacific persist to spring, which can hardly affect summer SIC anomaly in the Beaufort Sea. Therefore, the relationship collapses after the the early 2000s due to the weakened persistence of the eastern tropical Pacific SST anomaly.
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| 2. |
- Iyakaremye, Vedaste, et al.
(author)
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Increased high-temperature extremes and associated population exposure in Africa by the mid-21st century
- 2021
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In: Science of the Total Environment. - : Elsevier BV. - 0048-9697 .- 1879-1026. ; 790
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Journal article (peer-reviewed)abstract
- Previous studies warned that heat extremes are likely to intensify and frequently occur in the future due to climate change. Apart from changing climate, the population's size and distribution contribute to the total changes in the population exposed to heat extremes. The present study uses the ensemble mean of global climate models from the Coupled Model Inter-comparison Project Phase six (CMIP6) and population projection to assess the future changes in high-temperature extremes and exposure to the population by the middle of this century (2041–2060) in Africa compared to the recent climate taken from 1991 to 2010. Two Shared Socioeconomic Pathways (SSPs), namely SSP2-4.5 and SSP5-8.5, are used. Changes in population exposure and its contributors are quantified at continental and for various sub-regions. The intensity of high-temperature extremes is anticipated to escalate between 0.25 to 1.8 °C and 0.6 to 4 °C under SSP2-4.5 and SSP5-8.5, respectively, with Sahara and West Southern Africa projected to warm faster than the rest of the regions. On average, warm days' frequency is also expected to upsurge under SSP2-4.5 (26–59%) and SSP5-8.5 (30–69%) relative to the recent climate. By the mid-21st century, continental population exposure is expected to upsurge by ~25% (28%) of the reference period under SSP2-4.5|SSP2 (SSP5-8.5|SSP5). The highest increase in exposure is expected in most parts of West Africa (WAF), followed by East Africa. The projected changes in continental exposure (~353.6 million person-days under SSP2-4.5|SSP2 and ~401.4 million person-days under SSP5-8.5|SSP5) are mainly due to the interaction effect. However, the climate's influence is more than the population, especially for WAF, South-East Africa and East Southern Africa. The study findings are vital for climate change adaptation.
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| 3. |
- Yang, Xiaoye, 1996, et al.
(author)
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Enhanced spring warming of the Tibetan Plateau amplifies summer heat stress in Eastern Europe
- 2024
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In: Climate Dynamics. - 0930-7575 .- 1432-0894.
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Journal article (peer-reviewed)abstract
- The Tibetan Plateau (TP), often referred to as the “Roof of the World”, has experienced rapid warming in recent decades. This warming has had significant impacts on downstream regions, while its effects on upstream regions are less well-defined. This study explores the relationship between TP warming and the occurrence of summer heat stress days in Europe, with a particular focus on Eastern Europe (EEU). Our analysis reveals a robust correlation between TP warming in both the summer and the preceding spring, and the frequency of heat stress days in EEU, demonstrating a significant interannual connection. During the spring, pronounced warming in the southern TP generates a strong local Rossby wave source, triggering a substantial divergence anomaly that amplifies the warming effect. This mechanism weakens the subtropical jet and strengthens the polar jet during the summer, setting the stage for anticyclonic anomalies over EEU. Furthermore, anomalies induced by TP warming, characterized by local upward movement and divergence at upper levels, intensify convergence and sinking airflow in the upstream region, leading to increased adiabatic heating in EEU. The dynamic response of the summer circulation anomaly, exemplified by the anticyclone anomaly over EEU, to prior TP warming is further corroborated through numerical simulations.
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| 4. |
- Yang, Xiaoye, 1996, et al.
(author)
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Interdecadal variation of winter cold surge path in east Asia and its relationship with arctic sea ice
- 2020
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In: Journal of Climate. - 0894-8755. ; 33, s. 4907-4925
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Journal article (peer-reviewed)abstract
- The paths of winter cold surge (CS) events in East Asia (EA) from 1979 to 2017 are tracked by the Flexible Particle (FLEXPART) model using ERA-Interim daily datasets, and the probability density distribution of the paths is calculated by the kernel density estimation (KDE) method. The results showed that the paths of CSs are significantly correlated with the intensity of the CSs, which shows an interdecadal transition from weak to strong around 1995. CS paths can be classified into two types, namely, the western path type and the northern path type, which were more likely to occur before and after 1995, respectively. Before 1995, the cold air mainly originated from Europe and moved from west to east, and the synoptic features were associated with the zonal wave train. After 1995, cold air accumulated over western Siberia and then invaded EA along the northern path, and the synoptic features were mainly associated with the blocking structure. The geopotential height (GPH) anomalies over the Arctic were abnormally strong. This paper further analyzes the relationship between CSs and winter sea ice concentration (SIC) in the Arctic. The results show that the intensity of CSs is negatively correlated with the Barents SIC (BSIC). When the BSIC declines, the upward wave flux over the Barents Sea is enhanced and expanded to the midlatitude region. GPH anomalies over the Arctic are positive and form a negative AO-like pattern, which is conducive to the formation of the northern path CS. Furthermore, the observed results are supported by numerical experiments with the NCAR Community Atmosphere Model, version 5.3 (CAM5.3).
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| 5. |
- Yang, Xiaoye, 1996, et al.
(author)
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Phase-Locked Rossby Wave-4 Pattern Dominates the 2022-Like Concurrent Heat Extremes Across the Northern Hemisphere
- 2024
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In: GEOPHYSICAL RESEARCH LETTERS. - 0094-8276 .- 1944-8007. ; 51:4
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Journal article (peer-reviewed)abstract
- Concurrent heat extremes (CHEs) are becoming increasingly common in the mid-high latitudes across the Northern Hemisphere (NH), underscoring the need to comprehend their spatiotemporal characteristics and underlying causes. Here we reveal a phase-locking behavior in Wave-4 pattern, particularly after mid-1990s, giving rise to a prominent CHE mode akin to heat extreme pattern observed in 2022, which swept most NH regions. Wave-4 pattern significantly amplifies the likelihood of CHEs in Eastern Europe (similar to 30%), Northeast Asia (similar to 25%), and northwestern coast of North America (similar to 15%), while reducing the likelihood in central North America and northern Central Asia. During 1979-2022, the identified pattern accounted for over 69.7% of the trends in heat extremes over the mid-high latitudes of the NH, directly exposing approximately 333.5 million people to heat extremes. Observations and simulations indicate that radiation anomalies over Eastern European Plain and West Siberian Plain play pivotal roles as primary forcing sources for Wave-4 pattern. Researchers have found that concurrent heat extremes are becoming more common in the Northern Hemisphere. This study discovered that a specific weather pattern, called as Wave-4, became more prominent after the mid-1990s and is linked to these heat extremes. This pattern increases the probability of heatwave occurrences in Eastern Europe, Northeast Asia, and northwestern coast of North America while decreasing them in central North America and northern Central Asia. Between 1979 and 2022, the identified Wave-4 pattern contributed to more than two-thirds of the increase in heat extremes in the northern hemisphere, affecting around 333.5 million people. It is also determined that unusual radiation levels over the Eastern European Plain and West Siberian Plain are significant factors contributing to the Wave-4 pattern. This information helps us better understand the causes and characteristics of heat extremes in different parts of the world. The Phase-locked Rossby wave-4 pattern dominates the concurrent heat extremes across the Northern Hemisphere The identified pattern exposed approximately 333.5 million people to heat extremes Radiation anomalies over the Eastern European Plain and West Siberian Plain play pivotal roles as forcing sources of the pattern
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| 6. |
- Yang, Xiaoye, 1996, et al.
(author)
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Summer long-lived heatwaves in Northeast Asia promote heavy precipitation in South China
- 2024
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In: Atmospheric Research. - 0169-8095. ; 300
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Journal article (peer-reviewed)abstract
- Heatwaves interact with various extreme weather events, amplifying their impacts beyond the risks associated with high temperatures alone. However, previous research has often overlooked the extent to which heatwaves influence regions beyond their origin. In this study, we introduce a classification of heatwaves in Northeast Asia, distinguishing between long-lived heatwaves (LHWs) lasting five days or more and short-lived heatwaves (SHWs) lasting less than five days. The study highlights the significant role of LHWs in triggering heavy precipitation in South China. The anticyclonic anomalies associated with LHWs are influenced by a slow-moving wave train, initiating and sustaining cyclonic anomalies over South China, resulting in upward airflow anomalies. Additionally, easterly wind anomalies in the southern region of the anticyclonic anomalies facilitate moisture transport to South China, creating favorable conditions for precipitation. The findings underscore that LHWs could account for a noticeable portion (17.6%) of total summer extreme precipitation days in South China. The study highlights the significant role of LHWs-related circulations in triggering heavy precipitation in South China.
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| 7. |
- Zhang, Shiyue, et al.
(author)
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Potential impacts of reduced winter Kara Sea ice on the dipole pattern of cold surge frequency over the tropical western Pacific
- 2024
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In: ENVIRONMENTAL RESEARCH LETTERS. - 1748-9326. ; 19:6
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Journal article (peer-reviewed)abstract
- The impact of Arctic Sea ice melting on weather and climate extremes in the Northern Hemisphere has garnered widespread attention. Existing research has convincingly demonstrated the importance of this impact in mid-high latitudes, while its influence in areas beyond remains controversial. This study reveals the indirect influence of Kara Sea ice reduction on cold surge (CS) over the tropical western Pacific (TWP), with the East Asian jet stream serving as the connecting link. The leading mode of CSs over the TWP exhibits a zonal dipole characteristic, which is associated with cyclonic anomaly over the Philippine Sea. The enhanced cyclonic anomaly is caused by strengthened and northward-moved subtropical East Asian jet stream and weakened polar jet stream, which can lead to more CSs over the South China Sea and fewer CSs over the Philippine Sea. Such variations in the jet stream are contributed by the facilitated atmospheric blockings west of the Ural Mountains, which suppressed the circumpolar westerly winds and increased meridional temperature gradient in Northeast Asia. The connection between atmospheric blockings and Kara Sea ice can be confirmed through local vertical energy exchange. Simulations of the atmospheric response to the forcing of decreased Kara Sea ice support the proposed connection. Although there is no statistically significant correlation between tropical CSs and Kara Sea ice, this study highlights the potential impacts of Arctic climate change signal on weather and climate extremes over tropical regions.
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